The figure drawn below represents the energy levels of electrons
in an atom. The first shell holds maximum of 2 electrons in one
orbital; second shell holds maximum of 8 electrons in oneand
three
orbitals; third shell holds maximum of 18 electrons in one
, three
and five
orbitals; and so on.The 2 electrons in each orbital are
represented by up and down arrows.

The atomic number of potassium is 19, so it has nineteen
electrons. We apply the three rules to assign electrons into
orbitals according to the energy levels.

The first two electrons go in to the lowest-energy
orbital.
The next two and six electrons go into the second lowest-energy
orbital
and.
Similarly the next two and six electrons go into the third
lowest-energy orbital
and.
The remaining one electron goes to fourth lowest-energy
orbital.
So, the ground-state electronic configuration of potassium
is.

Therefore, potassium has only one electron in its outer most
shell.

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Step 2 of 3

(b)

Calcium atomic number is 20, so it has twenty electrons. We
apply the three rules to assign electrons into orbitals according
to the energy levels.

The first two electrons go in to the lowest-energy
orbital.
The next two and six electrons go into the second lowest-energy
orbital
and.
Similarly the next two and six electrons go into the third
lowest-energy orbital
and.
The remaining two electrons go to the fourth lowest-energy
orbital.
So, the ground-state electronic configuration of calcium
is.

Therefore, calcium has two electrons in its outer most
shell.

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Step 3 of 3

(c)

The atomic number of aluminum is 13, so it has thirteen
electrons. We apply the three rules to assign electrons into
orbitals according to the energy levels.

The first two electrons go in to the lowest-energy
orbital,
the next two and six electrons go into the second lowest-energy
orbital
and.
Similarly, the remaining two and one electrons go into the third
lowest-energy orbital
and.
So, the ground-state electronic configuration of aluminum
is.

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